Static solid state bioreactor and method for using same

ABSTRACT

A static solid state bioreactor and method of using same. The bioreactor comprises a vessel having an upper end and a lower end, the upper end having a sealable opening. A gas distribution system in communication with the upper end and the lower end of the vessel. A liquid distribution system in communication with the upper end of the vessel. A liquid recovery system in communication with the lower end of the vessel. A material removal system disposed at the lower end of the vessel for removing biomass from the vessel.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation application of co-pending U.S. patent applicationSer. No. 13/474,574, filed May 17, 2012, which is a continuation of U.S.patent application Ser. No. 12/423,803, filed Apr. 14, 2009, both ofwhich are incorporated herein by reference.

FIELD

The present patent document relates to static solid state bioreactorsand methods for using the same.

BACKGROUND

Fermentation may be broadly defined as the controlled cultivation ofmicroorganisms for the transformation of an organic compound into a newproduct. Therefore, the term “fermentation” includes conventionalalcohol fermentation, which is typically performed using some type ofliving ferment, such as yeast, and involves the enzymatically controlledanaerobic conversion of simple sugars, including those produced throughsaccharification, into carbon dioxide and alcohol. Depending on theorganic compounds employed and fermentative microorganism(s) employed,however, a host of other fermentation products may be generated inaddition to, or in the alternative to, alcohol.

Recently, conversion of biomass through fermentation into ethanol orother useful products as a replacement for fossil fuels has garneredconsiderable attention. Biomass for such conversion processes can bepotentially obtained from numerous different sources, including, forexample, wood, paper, agricultural residues, food waste, herbaceouscrops, and municipal and industrial solid wastes to name a few.

For a number of reasons, biomass is an attractive feedstock forproducing fossil fuel substitutes. Biomass has a smaller carbonfootprint than conventional fossil fuels because it typically comes fromplants that have an annual growth cycle; therefore, the carbon dioxideliberated by the combustion of the derived fuel is subsequently reusedthrough photosynthesis by the plant's regrowth and results in no netcarbon dioxide in the earth's atmosphere. Further, biomass is readilyavailable and the conversion of biomass provides an attractive way todispose of many industrial and agricultural waste products. Finally,biomass is a renewable resource because crops may be grown on acontinuous basis, utilizing the liberated carbon dioxide each cycle.

While biomass has the potential to provide an attractive fossil fuelalternative, substantial difficulties still remain. Because the mainproduct of the fermentation is a commodity, namely fuel, productioncosts must be extremely low to be competitive with other fuels. Inaddition, a main goal of using biomass as a fossil fuel replacement isto reduce carbon pollution. Therefore, any conversion process usedshould require low energy input. Because the United States aloneconsumes approximately nine (9) million barrels of gasoline each day,the process of creating a usable fossil fuel replacement from biomassmust be scalable to be a meaningful alternative.

Fermentation processes can be divided into two main categories, solidstate fermentation (SSF) processes and submerged liquid fermentation(SLF) processes. Solid state fermentation processes involve growth ofmicroorganisms on moist, solid biomass particles. The spaces between theparticles contain a continuous gas phase and a non-saturated waterphase. Thus, although droplets of water may be present between theparticles in a solid state process, and there may be thin films of waterat the particle surface, the inter-particle water phase is discontinuousand most of the inter-particle space is filled by the gas phase. Themajority of water in the system, therefore, is absorbed within the moistsolid particles. In submerged liquid processes by contrast, particlesare disposed in a continuous liquid phase.

Although SSF has been practiced for hundreds of years in the preparationof traditional fermented foods, its application to the production offermentation products within the context of modern biotechnology hasbeen fairly limited. This is because historically it has beennotoriously difficult to control the fermentation conditions within SSF.In practice, for example, temperature control, fluid channeling,excessive pressure drop, and evaporation have posed major problems tothe development of a commercially viable SSF reactor and process that issuitable for large scale, industrial applications. Thus, while theprocess of SSF has been practiced at small, batch, scale in the Asianfood and beverage industry for hundreds of years to make soy sauce andsake and research has been conducted more recently to produce otherproducts such as enzymes, most fermentation processes used today arestill carried out in SLF processes. Indeed, all commercial fermentationprocesses used for producing alternative fuels that exist today employ aSLF process.

Numerous drawbacks exist with using the SLF process, however. Twoprincipal drawbacks of SLF processes is that they tend to be capitalintensive and have high operating costs, making them less than optimumfor producing many fermentation products, including alternative fuels,such as ethanol, on an industrial scale and at a competitive price.

If the foregoing problems associated with SSF could be resolved, or atleast sufficiently ameliorated, a commercially viable SSF bioreactor andprocess that is suitable for large scale, industrial applications couldbe achieved. Such a SSF bioreactor and process could provide severaladvantages over existing SLF technologies, including high product yield,low cost, ease of use, and scalability.

A wide variety of apparatus have been tried as SSF bioreactors. Theseapparatus fall into two main categories: static systems and stirredsystems. Stirred systems have a means for mixing the biomass during thefermentation process. Stirring adds complexity and significant cost tothe bioreactor. This becomes especially true for a bioreactor devicethat is required to be scaled up to an industrial scale to support, forexample, the fossil fuel alternative market.

Static systems are sometimes used because the microorganism used in thefermentation process can not withstand the disruption caused duringstirring. Various static bioreactors for SSF have been designed and usedincluding, flasks, petri dishes, columns and trays. These designs havebeen mostly for laboratory use and are not effective or efficientlydesigned to be scaled for use at an industrial level.

One of the major problems in utilizing a static SSF bioreactor on alarge scale is temperature control. The fermentation of organiccompounds in general, and sugars contained or released from biomass inparticular, is an exothermic reaction, generating heat in the local areaof the microorganism performing the conversion. This leads to localizedelevated temperatures within the biomass in the reactor. The elevatedtemperatures within the SSF bioreactor can result in temperatures wellabove the optimum for microbial growth, which in turn can inhibit thefermentation process from occurring efficiently. Accordingly, a needexists for a SSF bioreactor design and method of using the same thatpermits temperature within the bioreactor to be maintained withinacceptable process limits during the conversion process.

When a large volume of reacting biomass is confined to a conventionalsolid state reactor, large temperature gradients are established withinthe biomass volume. This is primarily due to the fact that it isdifficult to remove the localized heat uniformly from the biomass usinga remote heat sink. For example, if the walls of the bioreactor are aheat sink, a temperature differential will form radially from the centeroutward towards the walls. With scale-up, the conduction effect of thewalls of the bioreactor will have little effect on the biomass in thecenter of the reactor and the radial temperature gradient will increase.

Temperature gradients also form in the axial direction. As thefermentation begins, heat from the exothermic reaction tends to rise.This creates a temperature gradient in the axial direction with the topof the biomass being hotter than the bottom.

In an attempt to control the temperature of the biomass, SSF bioreactorshave been designed with forced aeration. The convection and evaporationeffects of the gas as it passes through the biomass have been used toreduce the temperature. Air or gas is introduced at the bottom of thebiomass in the SSF and flowed to the top. By controlling the temperatureand humidity of the inlet gas, the biomass in the SSF can be cooled orheated respectively.

Numerous problems exist with present forced aeration bioreactor designs.First, the gas introduced at the bottom of the reactor tends to reducethe temperature of the biomass near the bottom of the reactor, but has alesser effect on the biomass as it passes up through the reactor. As gasis introduced, it absorbs heat from the biomass at the bottom of thereactor, which in turn raises the temperature and humidity of the gas,and makes it less effective at cooling as it passes up through thereactor. This tends to bring the temperature of the biomass at thebottom of the reactor into equilibrium with the temperature of the inputgas and creates an increasing temperature gradient as the height of thebiomass increases. These effects are exacerbated as the height of theSSF increases. Furthermore, the pressure drop typically increases as theheight increases making forced aeration more difficult.

Because of the problems with heat removal in forced aeration SSFbioreactors, the height of the bioreactor and therefore the height ofthe biomass has been kept low. It has been suggested that the height ofthe biomass in a forced aeration SSF bioreactor should not exceed one(1) meter. See D. A. Mitchell, et al., Solid State FermentationBioreactors, Fundamentals of Design and Operation, Chpt. 7, 93 (2006).This creates a problem, however, because by keeping the height small,large areas are required in order to scale up existing bioreactordesigns, which in many cases will be impracticable due to theavailability and/or cost of the required land.

One proposed solution to the height problem is suggested by Suryanarayanet. al. in U.S. Utility Pat. No. 6,664,095 B1. The Suryanarayan patentsuggest a tray stacking solution whereby the height of the biomass ineach individual tray is kept small and a plurality of trays are stackedon top of each other. While this solution effectively keeps the heightof the biomass small while allowing the bioreactor to increase inheight, the tray stacking design and implementation is too expensive andimpractical to scale to the industrial levels necessary for manypotential applications, including for cost effective alternative fuelproduction.

A further problem with forced aeration SSF reactors is the drying effectof the aeration process. The water content of the biomass must bemaintained. If the biomass becomes too dry, the efficiencies of thefermentation processes are reduced. Even if the gas entering thebioreactor is completely saturated, the biomass absorbs the moisturefrom the gas as it passes from the bottom of the bioreactor to the topand the resultant gas has a drying effect on the biomass. Further, theincrease in temperature towards the top of the bioreactor can causefurther evaporation, drying the biomass more.

In addition to the reduced efficiency of the fermentation processes, thedrying of the biomass has a secondary effect. As the bed dries it willcontract and reduce in volume. This reduction in volume will causechanneling and cause the biomass to pull away from the sides of thereactor. Channeling occurs when paths of lower resistance developthrough the bed and the forced aeration flows through the bed along thechannels only, rather than being evenly dispersed through the bed.Channeling can occur along the boundary between the reactor and thebiomass or through the biomass itself. Channeling reduces the flow ofgas to large parts of the volume of biomass causing localizedtemperature increases and an overall increase in the temperaturegradients and thus, a reduction in process efficiency. As the bioreactoris scaled up, the bioreactor walls, which can be used as heat sinks,have less intimate contact with the biomass, increasing the temperaturegradients in the radial direction.

Further, contemporary thinking is that liquid can not be effectivelyused in a static SSF bioreactor because the liquid can not be evenlydispersed throughout the biomass. The addition of liquid to static SSFreactors can result in flooding and inhibit the fermentation process.The permeability of biomass, depending on the source, is usually verylimited and tends to decrease as the biomass depth is increased.Further, as the biomass is fermented, the biomass degrades, its volumedecreases, and its density increases, further reducing permeability andinhibiting fluid flow.

Stirring or otherwise mixing the biomass in the bioreactor can reducechanneling, help eliminate temperature gradients, allow liquid to beadded to the biomass, and more evenly distribute the moisture in thereactor. While stirring can have positive effects, stirring mechanismsare complicated to build and become extremely expensive to construct andoperate when scaled. Even if stirring equipment on a large scale iseffectively designed, the process of stirring will be extremelyexpensive for a large scale SSF reactor. Wet biomass requires largeamounts of energy to mix or stir because of its weight. In addition, asmentioned above, stirring can have a deleterious effect on themicroorganisms used in the fermentation process.

In view of the foregoing, a need exists for an improved static solidstate bioreactor that addresses or at least ameliorates one or more ofthe problems associated with existing SSF bioreactor designs.

Saccharification is the process of breaking down a complex carbohydrate(such as starch, cellulose or hemicellulose) into its monosaccharidecomponents or sugars. Saccharification can be facilitated via the use ofchemical reagents, biological agents, or combinations of these two.During alternative fuel production processes, the converted biomass istypically subjected to a saccharification process prior to orsimultaneous with the fermentation process used to convert the simplesugars in the biomass, including those released throughsaccharification, into carbon dioxide and alcohol and/or methane.Accordingly, because one of the major potential applications of anindustrial scale static SSF bioreactor is the production of alternativefuels, such as ethanol and/or methane, it would be beneficial if such abioreactor could also be used for saccharification of biomass, eitherseparate from the fermentation process or simultaneous with thefermentation process.

SUMMARY OF THE INVENTION

In view of the foregoing, an object according to one aspect of thepresent patent document is to provide an improved static solid statebioreactor that may be used for solid state fermentation of biomass.Preferably the bioreactor is also suitable for saccharification ofcomplex carbohydrates in biomass. To this end, a static solid statebioreactor is provided that comprises: a vessel having an upper end anda lower end, the upper end having a sealable opening; a gas distributionsystem in communication with the upper end of the vessel and the lowerend of the vessel; a liquid distribution system in communication withthe upper end of the vessel; a liquid recovery system in communicationwith the lower end of the vessel; and a material removal system disposedat the lower end of the vessel for removing biomass residue from thevessel.

The bioreactor may further comprise a plurality of openings located onthe lower end of the vessel that allow the gas distribution system tocommunicate with the vessel. The liquid recovery system may alsocommunicate with the vessel through a plurality of openings on the lowerend of the vessel.

According to a further embodiment, the lower end of the vessel may beconically shaped. In one implementation, the lateral wall of theconically shaped lower end includes a plurality of openings to allowcommunication with the gas distribution system and/or the liquidrecovery system at the lower end. In such an embodiment, thecommunication with the gas distribution system and liquid recoverysystem can be spread out over a large area, namely the surface of theconically shaped lower end, while at the same time the biomass may bedirected towards a material removal system disposed at the apex of theconically shaped lower end. The conically shaped lower end, therefore,allows for even distribution of gas and liquid while facilitating easyand efficient material removal from the bioreactor.

According to a further embodiment, the material reclaim system of thebioreactor may comprise an auger driven by a motor. If for example thevessel is cylindrical, the auger may extend radially from the center ofthe vessel towards and outer wall and be rotateable around the vessel.In a second example, where the vessel has a conically shaped lower end,the auger may protrude into the vessel through a biomass opening at theapex of the conically shaped lower end and extend up towards a perimeterof the base of the conically shaped lower end. The auger would likewiserotate about the axis of the vessel drawing material down and towardsthe biomass opening at the apex.

According to yet another embodiment, the bioreactor comprises aplurality of screens, each screen being configured to fit within andcover one of the plurality of openings in the lower end. The screens areused to cover the openings and prevent biomass from escaping the vesseland entering the liquid recovery system or the gas distribution system.The screen spacing is preferably sufficiently small to substantiallyinhibit solids within the bioreactor from escaping through the screen,while at the same time allowing the free flow of liquid and gas throughthe screens. This prevents any biomass that might penetrate through thescreen from clogging the duct or tube used in the liquid recovery systemor gas distribution system.

According to a further embodiment, the screen used to cover the openingsin the lower end of the vessel comprises a wedge wire screen. The designof the wedge wire screen ensures that biomass does not get stuck in thespaces or holes between the wires of the screen but passes through. Thisprevents biomass from clogging the screen and preventing the passage ofgas or liquid through the screen.

According to a further embodiment, the screens used to cover theopenings in the lower end of the vessel can have wires running in adirection towards the biomass opening and material recovery system.Thus, in a conically shaped lower end, the screen wires would run fromthe apex to the perimeter of the base. Aligning the wires of the screensin the direction of material removal aids the material recovery systemand minimizes the likelihood of forming blockages in the screen as thesolids in the bioreactor move across the screen. If the wires run in aperpendicular direction, they can act like a grate, hampering materialremoval and increasing the likelihood that the screens will becomedamaged during operation of the bioreactor.

According to a further embodiment, the bioreactor's gas distributionsystem further comprises a first duct, a second duct, and at least onefan. The first duct is in communication with the upper end of the vesseland the fan and the second duct is in communication with the lower endof the vessel and the fan. The ducts can be made from a single piece ora plurality of pieces. The ducts allow the fan to communicate with theupper and lower ends of the vessel. Preferably the gas distributionsystem comprises one or more valves for selectively connecting theintake and output of the fan to the first and second ducts,respectively, thereby allowing the gas distribution system to change thedirection of gas flow through the vessel.

According to a further embodiment, the liquid distribution system of thebioreactor may be in communication with the liquid recovery system. Byconnecting the liquid distribution system with the liquid recoverysystem, liquid effluent from the biomass can be recycled. Because theeffluent from the biomass may contain sugars or other organic compoundsthat have not been fermented yet, recycling the liquid effluent allowsfor a more complete and efficient fermentation process.

According to another aspect of the present patent document, a method ofperforming static solid state fermentation is provided. The methodcomprises: mixing a bulking agent with biomass; adding the mixture to astatic solid state bioreactor; irrigating the mixture with an aqueoussolution; flowing gas through the mixture; and maintaining amicroorganism supporting environment within the bioreactor by managingthe flow of the aqueous solution and the gas through the mixture andperiodically switching the direction of gas flow through the bioreactor.

Prior to adding the mixture to a static solid state bioreactor a numberof additives and reagents may be added to the biomass to improve orsupplement fermentation of the biomass including: 1) adding an inoculumcomprising one or more microorganism to the biomass; 2) adding one ormore enzymes to the biomass; and 3) adding an antibiotic to the biomass.

Once the biomass is prepared for fermentation and the mixture is addedto the bioreactor, the mixture may be irrigated with water to maintain adesired moisture content within the biomass or to heat or cool themixture. Aqueous solution that flows through the biomass is dischargedinto the fluid recovery system, which collects the effluent dischargeand may recycle it back onto the biomass within the bioreactor.

In order to allow fluid flow through the biomass (both gas and liquid)it is desirable that a certain hydraulic conductivity be maintainedwithin the reactor throughout the fermentation process. This isaccomplished through the use of the bulking agent. Preferably, thecomposition, size, and amount of bulking agent mixed with the biomass isselected to maintain a hydraulic conductivity of the biomass greaterthan 10⁻⁴ cm/sec throughout the fermentation process.

According to yet another aspect, a non-stirred solid state bioreactor isprovided that comprises, a hollow body in which a mixture of biomass anda bulking agent is stacked. The stacked biomass is stored within thehollow body under conditions suitable for fermentation. The hollow bodyhas a lower end and an upper end. The lower end is perforated to allowthe flow of gas and liquid through the stacked biomass. The upper endhas at least one sealable opening for stacking the biomass within thehollow body. A passageway for removal of the decomposed biomass materialis provided at the lower end of the hollow body. A material removalsystem is operatively provided within the hollow body at the lower end.The material removal system is configured to direct the flow ofdecomposed biomass material toward the passageway during unloading ofthe hollow body. A gas delivery system is coupled to the upper and lowerends of the hollow body and is configured to flow gas through thestacked biomass in both directions, from the lower end to the upper endand from the upper end to the lower end. An irrigation system isdisposed within the hollow body proximate to the upper end of the hollowbody and is configured to irrigate the stacked biomass from above. Asystem for collecting liquid effluent that drains from the stackedbiomass is operatively provided proximate to the perforated lower end.

According to one embodiment, the material removal system comprises atleast one auger to remove the material from the hollow body.

In yet another embodiment, the vessel may be sealed for anaerobicbioreactor operation.

According to yet another aspect of the present patent document, abioreactor for performing static solid state fermentation of biomass isprovided. The bioreactor according to this aspect comprises, a vesselhaving an upper end and a lower end, the lower end having a plurality ofopenings and a material removal port. A plurality of gas ports are incommunication with a gas distribution system and in communication withthe plurality of openings in the lower end of the vessel. A plurality ofliquid ports are in communication with a liquid collection system and incommunication with the plurality of openings in the lower end of thevessel. At least one screen is disposed in the lower end of the vesselcovering the plurality of openings.

In one embodiment, the bioreactor may further comprise a plurality ofmanifolds, the plurality of manifolds being disposed to connect theplurality of openings with the plurality of gas ports and the pluralityof liquid ports. Preferably at least one gas port is located above atleast one liquid port on at least one manifold. This allows the liquidto naturally separate from the gas and enter the liquid recovery systemwhile minimizing the amount of liquid that enters the gas distributionsystem.

As described more fully below, the static solid state bioreactor designsand methods for using same may readily and cost effectively be scaledfor large industrial applications such as biofuels production. Furtheraspects, objects, desirable features, and advantages of the bioreactorsand methods disclosed herein will be better understood from the detaileddescription and drawings that follow in which various embodiments areillustrated by way of example. It is to be expressly understood,however, that the drawings are for the purpose of illustration only andare not intended as a definition of the limits of the claimed invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates a bioreactor for performing staticsolid state saccharification and/or fermentation of biomass.

FIG. 2 illustrates a cross sectional view of a vessel for use in abioreactor for performing static solid statesaccharification/fermentation of biomass with a material removal systemfurther comprising at least one auger.

FIG. 3 schematically illustrates a bioreactor for performing staticsolid state saccharification and/or fermentation of biomass.

FIG. 4 is a schematic illustrating one embodiment of a gas distributionsystem for the bioreactor shown in FIG. 3.

FIG. 5 illustrates a perspective view of a bioreactor vessel with aconical lower end.

FIG. 6 illustrates a perspective view of a conically shaped lower endwith a plurality of openings for gas and liquid distribution/collection.

FIG. 7 illustrates a cross section of a screen as used in FIG. 6.

FIG. 8 illustrates a cross section through one of the manifolds shown inFIG. 6 for attaching the liquid recovery system and the gas distributionsystem to the lower end of the vessel.

FIG. 9 illustrates a plurality of manifolds attached to a plurality ofopenings on the lateral surface of the lower end of the vessel.

FIG. 10 illustrates a perspective view of an alternative embodiment of alower end.

FIG. 11 illustrates a perspective view of another embodiment of a lowerend.

FIG. 12A illustrates yet another embodiment of a conically shaped lowerend for the bioreactor of FIG. 5.

FIG. 12B illustrates a perspective view of a screen panel design for usein the lower end of FIG. 12A.

FIG. 13A illustrates still a further embodiment of a conically shapedlower end for the bioreactor of FIG. 5.

FIG. 13B illustrates a perspective view of a screen panel design for usein a vertically oriented panel frame designed lower end for abioreactor.

FIG. 13C illustrates an enlarged cross-sectional view shown inperspective of the portion of the screen circled in FIG. 13B.

FIG. 14 is a graph showing the effect of bulking agent volume ratio toacceptable bed height in fermentation of waste paper based on irrigationrate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following description of the preferred embodiment, reference ismade to the accompanying drawings that form a part hereof, and in whichis shown by way of illustration a specific embodiment in which theinvention may be practiced. It is to be understood that otherembodiments may be utilized and structural changes may be made withoutdeparting from the scope of the present invention.

Consistent with its ordinary meaning as a renewable energy source, theterm “biomass” is used herein to refer to living and recently deadbiological material including carbohydrates, proteins and/or lipids thatcan be converted to fuel for industrial production. By way ofnon-limiting example, “biomass” can refer to plant matter, biodegradablesolid waste such as dead trees and branches, yard clippings, recycledpaper, recycled cardboard, and wood chips, plant or animal matter, andother biodegradable wastes.

FIG. 1 illustrates a schematic view of a bioreactor for performingstatic solid state saccharification and/or fermentation of biomass.Bioreactor 100 comprises vessel 10, gas distribution system 30, liquiddistribution system 50, liquid recovery system 70, and material removalsystem 90.

As shown, vessel 10 has a cylindrical shape. Cylindrical is a preferredshape as it facilitates the design of a suitable material removal system90. The vessel 10, however, is not limited to any particular shape andmay be, for example, square, triangular, rectangular, octagonal, or anyother suitable multi-sided shape or hollow body without departing fromthe scope of the present invention. Vessel 10 can be made from variousmaterials, or material combinations, including, stainless steel, steel,aluminum, other metals, concrete, wood, plastic or plastic derivatives,or other basic building material.

Vessel 10 may be constructed using any construction techniques suitablefor large vessels. Depending on its size, for example, vessel 10 may beconstructed from a single piece or from a frame and liner typeconstruction. If the vessel 10 is to be used for an anaerobicfermentation process, such as the production of alcohol or methane, thenthe vessel 10 is preferably sealable to provide a gas-tight environment,as maintaining an anaerobic environment in such processes is critical toachieving an efficient bioreactor 100.

While vessel 10 can be any size, the vessel 10 is preferably of a sizesuitable for industrial scale. Accordingly, the vessel 10 preferably ispreferably greater than 1 meter high and greater than 1 meter indiameter. More preferably, the height of vessel 10 is 3 meters orhigher, and even more preferably 6 meters or higher. The diameter of a 6meter vessel 10 may be, for example, greater than 9 meters or greater indiameter and even more preferably 15 meters or greater in diameter.Common existing structures may be retrofitted to make them gas tight foruse as vessel 10, including large tanks, covered lagoons, grain silos,or other large enclosures.

Vessel 10 comprises a lower end 12 and an upper end 14. Vessel 10further comprises a sealable opening 16 in the upper end 14. Thesealable opening is used for loading the biomass into the vessel 10. Thebiomass can be loaded via a tripper conveyor or screw feeder dischargingthrough the sealable opening 16 in the upper end of the vessel 10. Theopening 16 may be sealed using automatic doors to create an anaerobicenvironment.

Before the biomass is loaded into the vessel 10 for fermentation, anumber of reagents and additives may be added. For example, theproduction of alternative fuels from biomass may require additionalprocesses, other than fermentation, such as saccharification.Saccharification may be required if the biomass does not already containsufficient free fermentable sugars. Saccharification can be induced byadding enzymes to release the sugars for further fermentation. Theenzymes hydrolyze the complex sugars present in the biomass, convertingthem to simple fermentable sugars. Depending on the biomass to beconverted, different amounts or combinations of enzymes may be needed.Saccharification and fermentation can occur simultaneously in thebioreactor or in series. Different types of biomass may require theaddition of different additives before entering the bioreactor.

Once the biomass contains free fermentable sugars, the actualmicroorganism, ferment or fermentation agent, can begin to convert thefree fermentable sugars to alcohol, such as ethanol, or methane. Thefermentation agent in the context of alcohol fermentation is typically ayeast that converts the simple sugars into ethanol.

The fermentation agent may require the addition of nutrients for moreefficient propagation. Blended complex yeast nutrients that supplyammonia salts, alpha amino nitrogen, sterols, unsaturated fatty acids,other key nutrients, and inactive yeast are commercially available.

In order to suppress the proliferation of undesirable microorganisms,that produce unwanted products and reduce ethanol yield, one or moreantibiotic substances can be added. Once the biomass is prepared withthe additives and reagents a bulking agent can be added to increase andmaintain the hydraulic conductivity of the biomass.

As shown in FIG. 1, bioreactor 100 further comprises a material removalsystem 90 disposed at the lower end 12 of the vessel 10. The materialremoval system is used to remove the biomass residue from the vessel 10when saccharification and fermentation has finished. The materialremoval system can be designed in a number of ways. If the vessel issuspended above the ground, a hinged base plate(s) could be used to dumpthe material out of the vessel 10. A portion of the side of the vessel10 along the lower end 12 could be opened and a mechanical device, suchas a backhoe, could be used to remove the biomass residue. A tube couldbe inserted through a hole in the lower end 12 and the biomass could bevacuumed out.

Although FIG. 1 shows but a single instance of a bioreactor 100,numerous instances can be used in combination. In particular, aplurality of vessels 10, gas distribution systems 30, liquiddistribution systems 50, liquid recovery systems 70, and materialremoval systems 90 can be used and interconnected. Not only can theoverall design be duplicated, but individual components can likewise beduplicated. For example, a plurality of vessels 10 could be used incommunication with a single gas distribution system 30, and liquiddistribution system 50.

FIG. 2 illustrates a cross sectional view of a vessel 10 for use in abioreactor for performing static solid state saccharification and/orfermentation with a material removal system further comprising at leastone auger. As shown in FIG. 2 a vessel 10 has a material removal system90 further comprising an auger 92. The auger is located at the lower end12 of the vessel 10 and can rotate around the vessel 10 drawing biomasstowards the center and out through an opening into a hopper 96. Thehopper 96 is not required and the material could be removed directlyinto a truck or onto a conveyer for transport. If a hopper 96 is used asecond auger (discharge auger) 94 may be employed to remove the materialfrom the hopper 96. Material removal systems similar to the onesdescribed can be obtained from Laidig Systems, Inc. 14535 Dragoon Trail,Mishawaka Ind. 46544.

The biomass conversion reactions generate heat but they may also requirea specific temperature to initiate. This presents a new problem becausethe SSF reactor has to be heated to its ideal starting temperaturebefore significant conversion reactions will take place. Therefore,sometimes it may be advantageous to be able to restrict heat loss fromthe bioreactor.

As shown in FIG. 2, in order to help prevent heat loss, the walls 11 ofthe vessel 10 may be insulated to better control the temperature in thebioreactor 10. The outside of the vessel 10 will be a heat sink if thewalls 11 are not insulated and radial temperature gradients may form.The walls can be insulated on the inside as shown in FIG. 2, or on theoutside. Insulation can be made from common insulation materials such asblankets, spray foams, fiberglass, or other materials that can be usedto cover, line, or separate the walls of the reactor from the biomassand prevent or reduces the passage, transfer, or leakage of heat.

As well as passive heat protection such as insulating the walls, thebioreactor may employ active heating like an electric heater.

Returning to FIG. 1, the bioreactor 100 further comprises a gasdistribution system 30 for flowing a gas through the vessel 10. Thefermentation of sugars produces ethanol and carbon dioxide. Theatmosphere in the newly-loaded bioreactor 100 starts off as air but asfermentation proceeds, the carbon dioxide generated rapidly displacesthe air, resulting in an essentially complete carbon dioxideenvironment. Alternatively, the initial air atmosphere in the bioreactor100 may be displaced by introducing carbon dioxide from an outsidesource. One example would be from an adjacent bioreactor.

A gas distribution system 30 helps manage the heat and controltemperatures in the bioreactor 100 and maintains the desired gaseousenvironment for saccharification and fermentation. In addition, the gasdistribution 30 system is an integral part of collecting the product ofthe biomass conversion.

The gas leaving the solid state bioreactor will contain much of thedesired product of the biomass conversion. The low vapor pressure of thealternative fuels produced in the bioreactor tend to cause them toevaporate into the gas stream at levels proportionate to theirconcentration in the bioreactor liquid phase. The higher the temperatureand the higher the liquid fuel concentration, the greater the effect.

The gas distribution system 30 is in communication with the upper end 14and the lower end 12 of the vessel 10, via duct 46 and can force a flowof gas from the lower end 12, through the vessel 10, and out the upperend 14. As shown in FIG. 1, the gas distribution system 30 is incommunication with the lower end 12 of the vessel 10 through a pluralityof openings 18.

Combined with the gas distribution system 30, the natural evolution ofwarm carbon dioxide during fermentation results in an upward gas flow ofgas in the vessel 10. This gas flow carries with it heat and moistureand causes a axial temperature gradient to form in the vessel 10 suchthat the biomass in the upper end 14 is hotter than the biomass in thelower end 12. Utilizing a downward forced gas flow allows the gas to beremoved from the lower end 12 of the vessel 10 and mitigates thetemperature gradient. Therefore, in the preferred embodiment, the gasdistribution system 30 can also reverse the direction of the flow of gasthrough the vessel 10 to enter at the upper end 14 and exit from thelower end 12 of the vessel 10.

FIG. 3 illustrates a schematic view of a bioreactor for performingstatic solid state fermentation of biomass. As shown in FIG. 3, the gasdistribution system further comprises a duct 46, at least one fan 34,and at least one valve 38, 40, 42, and 44. The gas distribution system30 is in communication with the upper end 14 and the lower end 12 of thevessel 10 via duct 46. Duct 46 may be comprised from a single unit ormanufactured from several units. The duct 46 can be made from metalpiping, PVC or other plastic piping, conduit, or any other type of tube,canal, pipe, or conduit by which a gas or air can be conducted orconveyed.

The gas distribution system further comprises at least one fan 34 toforce the gas through the vessel 10. The at least one fan 34 couldlikewise be a blower or any other type of device for producing a currentof gas or pressure differential, within a duct 46. A single fan or aplurality of fans may be used in the final form. As shown in FIG. 3, asingle fan 34 is used for forcing the gas through the vessel 10. Inaddition to fan 34, an additional fan 35 is shown in the embodimentillustrated in FIG. 3 to allow the bleeding of any excess gas in the gasdistribution system 30.

As shown in FIG. 3 four (4) valves 38, 40, 42, and 44 are used but anynumber of valves may be used in combination to direct the flow of gasthrough the vessel 10. As shown in FIG. 3 the four (4) valves 38, 40,42, and 44 allow the gas distribution system 30 to control the flow ofgas through the vessel 10 and change the direction of gas flow.

If valves 38 and 42 are closed and valves 40 and 44 are open, the gasleaving the at least one fan 34 is forced through the duct 46 and intothe upper end 14 of the vessel 10. The gas continues through the biomassand out the lower end 12 of the vessel 10 returning back to the at leastone fan 34. If valves 38 and 42 are open and valves 40 and 44 areclosed, the gas is forced to flow in the opposite direction, enteringthe lower end 12 of the vessel 10 and flowing through the biomass andout the upper end 14 before returning back to the at least one fan 34.

While not required in the composition of a gas distribution system 30,the gas distribution system 30 may further comprise a condensation trap36, and a liquid trap 32. As shown in FIG. 3, a condensation trap(knock-out pot) 36 may be placed in communication with the duct 46 tocontrol the humidity of the gas and condense out the desired product,such as ethanol, from the gas. The liquid trap (moisture trap) 32, maybe used in a similar manner and may also prevent liquid contamination ofthe gas stream during downward gas flow.

FIG. 4 is a schematic illustrating a gas distribution system 30 that canreverse the flow of gas to the vessel 10. As shown in FIG. 4, oneembodiment of the gas distribution system 30 that can reverse the flowof gas to the vessel 10 further comprises three (3) fans 33, 34, and 35,and ten (10) valves 37, 38, 39, 40, 41, 42, 43, 44, 45, and 47. Fans 33,and 34 are used in combination to produce the flow of gas through thevessel 10 via duct 46. Valves 39, 41, 43 and 45 are isolation valvesadded to prevent back pressure from reversing the flow of gas into thefans 33 and 34. Valves 38, 40, 42, and 44 control the direction of flowthrough the vessel 10 as described above. Gas enters the fans from thecondensation trap (knock-out pot) 36 which can be used to removecondensed liquid. Valves 43 and 45 can regulate the flow of gas into thefans 33 and 34 respectively so that either fan can be used or both canbe used. Gas leaving the vessel 10 is returned to the condensation trap36 to complete the recycling loop.

In order to make the fermentation process in the bioreactor 100 moreefficient, it is sometimes advantageous to heat the biomass. Addingoxygen can accelerate reactions in the bioreactor and provide additionalheat from within. Therefore, in addition to the passive and activeheating methods described above, when additional energy is needed,oxygen can be introduced by bleeding air into the gas distributionsystem 30 through a bleed valve 37. Thus it is possible to heat thebiomass and control the temperature during the ethanol production phase.Excess gas can be removed from the system through a vent fan 35. Valve47 can be used to control the removal of excess gas by the vent fan 35.Valve 37 can be utilized to allow air into the system to enhanceoxidation reactions and provide heat. Valve 47 and fan 35 show oneembodiment of a system utilized to bleed excess gas from the system.Excess gas can be directed to a newly-loaded bioreactor to purge theinitial air atmosphere and replace it with carbon dioxide.

Returning again to FIG. 1, the bioreactor 100 further comprises a liquiddistribution system 50 and a liquid collection system 70. The liquidcollection system 70 is disposed at the lower end 12 of the vessel 10.Once the biomass is loaded into the vessel 10 the saccharificationand/or fermentation processes may begin by introducing water to thebioreactor to initiate effluent discharge. The effluent discharge iscollected through a plurality of openings 18 located on the lower end 12of the vessel 10 by the liquid collection system 70.

The effluent discharge contains ethanol, water, and unfermented sugars.Returning to FIG. 3, the effluent discharge may be collected in a tank72. As shown in FIG. 3, fluid collection system 70 may further comprisean additional storage tank 74. Additional storage tanks can be used tostore excess effluent discharge but are not required.

When sufficient effluent discharge is collected by the liquid collectionsystem 70, it can be added back to the biomass in the vessel 10 byconnecting liquid collection system 70 with the liquid distributionsystem 50. The liquid distribution system 50 may further comprise anirrigation system 52 located at the upper end 14 of the vessel 10.Preferably the irrigation system is a drip irrigation system but canalso be a sprayer or other nozzle type that can effectively distributethe effluent discharge over the surface of the biomass located at anupper end 14 of the vessel 10. The liquid distribution system 50 mayfurther comprise a pump 54. The pump 54 is in communication with theeffluent discharge in the tank 72. The pump 54 can recycle the effluentdischarge from the fluid collection system 70 to the fluid distributionsystem 50. Recycling effluent discharge allows the sugars that have notbeen broken down to be re-injected into the vessel 10 for completefermentation of the remaining sugars. Recycling effluent discharge alsoallows the recycle of unreacted reagents such as enzymes. Tank 72 alsoacts as a gas seal and prevents the process gas from leaving via theliquid distribution system. This is accomplished by maintaining adesired hydraulic head in the tank above the discharge of the liquidinto the tank that is greater than the gas pressure in vessel 10.

In addition, when the liquid effluent solution is recycled, it may betreated to remove or inactivate deleterious constituents. This can beaccomplished by either using a physical filter or by chemical treatment.

In addition to recycling the effluent discharge, the liquid distributionsystem 50 may be in communication with a plurality of solution tankscontaining additives helpful in the saccharification and/or fermentationprocess. This allows the use of the liquid distribution system to injectimportant ingredients into the biomass whenever they are needed. Theseingredients can be new cultures of microbes, enzymes, nutrients, water,antibiotics, or other essential ingredients to the saccharificationand/or fermentation processes.

In addition to the ability to inject important ingredients into thebioreactor 10 and recycle the effluent discharge, the liquiddistribution system 50, the liquid collection system 70, and the gasdistribution system 30 play important roles in temperature control.Temperature control is a key issue in saccharification and yeastfermentation. The optimum temperature for yeasts used in sugarfermentation such as Saccharomyces cerevisiae is approximately 35°Celsius. At high temperatures the yeast dies and at low temperatures theyeasts' activity is reduced.

During the start of the saccharification and/or fermentation process amethod of “bootstrapping” the temperature up can be practiced. At thisearly stage of the process the temperature may be below the optimum andheat needs to be conserved until the operating temperature is reached.

In order to control the temperature within the vessel 10, the bioreactor100 of the present invention balances countercurrent liquid and gasflows. Ambient temperature solution is applied to the top of the biomassby the liquid distribution system 50 at the upper end 14 of the vessel10. The solution is warmed by heat exchange with the warm gas leavingthe biomass. The gas undergoes reflux due to cooling at the biomasssurface and condenses moisture giving up its heat of condensation to thebiomass. As the solution flows downward, it absorbs heat from thebiomass and reaches thermal equilibrium. At the lower end 12 of thevessel 10 the incoming cool ambient gas is humidified and the solutionleaves the biomass with less energy. The heat capacity of the liquidstream and the gas stream are calculated and the relative flow ratesadjusted to maintain the desired temperature and temperature profile.

The relative flow rates of gas and fluid can be expressed as adimensionless ratio Ga/Gl. This is the ratio of the flow rate of theupward heat carrying gas stream, to the flow rate of the downward heatcarrying liquid stream. The flows are expressed as mass per unitcross-sectional area of the reactor per unit time, or commonly askilograms of fluid per square meter of reactor cross-sectional area perhour (kg/m²/hr). The Ga/Gl ratio is typically and preferably keptbetween 0.25 and 0.4 depending on what stage the reaction process is in.

Darcy's law is often used to express the flow of liquid through a porousmedium. A general form of the equation:

$Q = {{- {AK}}\frac{h}{l}}$Q = total  discharge (units  m³/s)K = hydraulic  conductivity (units  m/s)A = cross-sectional  area  to  the  flow (units  m²)

dh/dl=is a change in hydraulic head Δh over the length L, limit of Δh asL goes to zero.

Hydraulic conductivity is related to permeability and when a fluid otherthan water at standard conditions is being used, the conductivity may bereplaced by the permeability of the media. The two properties arerelated by:

K=kρg/μ=kg/v

k=permeability, (m²),μ=fluid absolute viscosity, (N s/m²) andv=fluid kinematic viscosity, (m²/s).Substitution of permeability for hydraulic conductivity back intoDarcy's law yields:

$Q = {{- A}\frac{{k\; \rho \; g}\;}{\mu}\frac{h}{l}}$

The hydraulic conductivity of the biomass to gas and liquid can begreatly increased by mixing a bulking agent with the biomass prior toloading into the bioreactor 100. The addition of a bulking agent helpsmaintain the hydraulic conductivity, counteracting the effects ofcompaction of the biomass under its own weight and breakdown of thebiomass during conversion. The increased hydraulic conductivityeliminates channeling and also prevents the biomass from dramaticallyreducing in volume as the saccharification and/or fermentation processesoccur. This prevents the biomass from pulling away from the walls of thebioreactor, another common cause of channeling.

Hydraulic conductivity is a key factor in the effectiveness of thetemperature control of the gas distribution system 30 and the liquiddistribution system 50. Adequate hydraulic conductivity is required toensure that the flows of both gas and liquid can be maintained at thedesired levels for the duration of the conversion process.

Bulking agents can be either degradable or non-degradable and caninclude, for example: sized aggregate, Styrofoam “peanuts” (preferablyclosed cell), plastic balls, almond shells and hulls, shredded tires,wood chips, and corn cobs. The selection of a bulking agent will dependon numerous factors including availability and also the type of biomassthe bulking agent is to be mixed with. When selecting a bulking agent itis important to consider whether it will be inert with respect to thecontents of the bioreactor or not. The influences of bulking agents thatwill somehow participate in the reactions taking place in the bioreactormust be accounted for.

Any bulking agent that when combined with the biomass, can pass thedesired liquid and gas flows when under pressure, can be used. It isdesired to maintain the ultimate hydraulic conductivity of the biomassto be greater than 10⁻⁵ cm/sec. More preferably the ultimate hydraulicconductivity of the biomass should be maintained greater than 10⁻⁴cm/sec which will generally limit the gas flow back-pressure to adesired maximum of less than 200 mm of water head. The ultimatehydraulic conductivity is measured at the end of life, after thereactions in the bioreactor have finished. In this manner, it can beverified that the biomass bulking agent mixture maintain the necessaryhydraulic conductivity throughout the life of the reaction in thebioreactor.

The quantity of bulking agent added will depend on the bulking agentparticle size, size distribution, aspect ratio, shape, type anddegradation rate. Table 1 lists some possible bulking agents (BA) tobiomass (or feedstock) ratios that were found to have suitable hydraulicconductivity for processing in the bioreactor 100 of the presentinvention.

TABLE 1 Bulking Agent to Biomass Ratio Bulking *Bulking *Substrate RatioColumn Agent Substrate Agent (g) (g) (BA:BM) Size Note Plastic Ballscardboard 500 230 2.2 1 1 m Plastic Balls cardboard 250 450 0.6 1 1 mPlastic Balls cardboard 200 450 0.4 1 1 m Plastic Balls cardboard 200400 0.5 1 1 m Plastic Balls cardboard 250 500 0.5 1 1 m Plastic Ballscardboard 450 900 0.5 1 3 m Tires cardboard 700 450 1.6 1 1 m Tirescardboard 584 450 1.3 1 1 m Tires cardboard 600 450 1.3 1 1 m Tirescardboard 400 450 0.9 1 1 m Tires cardboard 300 450 0.7 1 1 m Tirescardboard 1500 1800 0.8 1 3 m Tires cardboard 750 1800 0.4 1 3 m Tirescardboard 750 2000 0.4 1 3 m Plastic Balls Sludge 300 460 0.7 1 1 mPlastic Balls Sludge 300 500 0.6 1 1 m Packing Sugar Beet 5.46 7500.00728 1 BC-1 or 1:1 by Peanuts Pulp volume Almond Shells Sugar Beet362 362 1 1 BC-2 Pulp Almond Shells Fresh Beets 2000 8750 0.2 1 BC-3Almond Shells Fresh Beets 2000 8750 0.2 1 BC-4 Packing Fresh Beets 0.5 1** BC-5 **Based on Peanuts volume *Note: Bulking Agent and Substrateweights are “as received”

Typical bulking agent to biomass mass ratios that have proven effectivefor use in the bioreactor 100 range from 1:5 to 1:1. The correspondingvolume ratios will depend on the relative bulk densities of the biomassand bulking agent. Although larger ratios of bulking agent to biomasswill tend to have better hydraulic conductivity for any given system,increased use of bulking agent will result in reduced volume of biomassthat can be placed in the reactor.

As noted above, the bulking agent to biomass (or feedstock) volume ratioinfluences the permeability in solid state fermentation. The graph inFIG. 14 shows the effect of bulking agent volume ratio to acceptable bedheight in fermentation of waste paper based on irrigation rate for theexperimental data in Table 2 below. As FIG. 14 shows, increasing SSF bedheight requires an increased bulking agent to substrate volume ratiobecause of the increased bed self-weight. In FIG. 14, “Pass” and “Fail”refers to the hydraulic conductivity of the feedstock bed in the SSFreactor. In other words, it is considered to pass if liquid and gas canflow freely through bulked feedstock. The maximum acceptable “pass”irrigation rate for a given bed height is given in Table 2 and generallyincreases with bed height due to the increased volume and thus increasedirrigation rates that are required to maintain the bed within anacceptable process temperature range.

TABLE 2 Effect of Bulking Agent Ratio on Acceptable Bed Height WeightVolume SSSF Irr. Ratio Ratio Ht Rate Bulking Agent Substrate (BA:BM)(BA:BM) (m) (L/m²/h) Plastic Balls Waste Paper 0.00:1 0.00:1 0.3 5Plastic Balls Waste Paper 0.44:1 0.29:1 1 5 Plastic Balls Waste Paper0.50:1 0.35:1 3 30 Packing Waste Paper 0.00:1 0.37:1 4 30 Peanuts

Preparing similar tables for other bulking material/feedstock systemswill show that the “pass/fail” curve shown in FIG. 14 will shift asillustrated depending on a number of parameters. For example, decreasingfeedstock particle size requires a higher bulking agent ratio due to thelower void volume and lower coefficient of permeability of thefeedstock. Likewise, feedstocks with high aspect ratios (flat as opposedto round) also require a higher bulking agent ratio. On the other hand,feedstocks that digest completely tend to require a lower bulking agentratio as the bed voidage increases as the reaction proceeds.

For any given system and reactor bed height, it is desirable to operateas close as possible to the boundary line shown in FIG. 14 in order tomaximize the volume of the biomass feedstock that can be included in thebioreactor. Accordingly, the volume of the employed biomass ispreferably less than 20%, and more preferably less than 10%, greaterthan that required by the boundary line for a given material system andbed height.

Although FIG. 14 has been prepared based on irrigation rate, a similarPass/Fail curve may be prepared based on acceptable “pass” gas flowrates for a given bed height and material system.

The bulking agent can be mixed with the biomass prior to loading intothe vessel 10. A variety of mixing devices can be employed including asimple screw mixer, commercial agricultural feed mixer. The goal of themixing device is to have an evenly distributed mix of bulking agent andbiomass.

FIG. 5 illustrates a perspective view of a vessel for static solid statesaccharification and/or fermentation with a conical lower end 12. Theconical lower end 12 further comprises a biomass opening or passageway13 located at the apex of the conical lower end 12. A material removalsystem 90 further comprises an auger 92 driven by a motor 93 protrudingthrough the biomass opening 13 towards the perimeter of the base of theconically shaped lower end 12. The auger 92 can rotate around theconically shaped lower end 12 to remove biomass from the vessel 10. Oneadvantage of the conically shaped lower end is that it facilitates thenatural progression of biomass towards the biomass opening 13 at theapex of the conically shaped lower end 12.

FIG. 6 illustrates a perspective view of a conically shaped lower endwith a plurality of openings. As shown in FIG. 6, the conically shapedlower end 12 can further comprise a plurality of openings 18 located onthe lateral surface. The plurality of openings 18 are used to allow thevessel 10 to communicate with the liquid recovery system 70 and the gasdistribution system 30. As shown in FIG. 6, the openings are circular;however, the openings can be any shape including, square, rectangular,triangular or other shape. Preferably the openings may be round as itmakes attachment of a manifold for communication with the liquidrecovery system 70 and gas distribution system 30 easier. As shown inFIG. 6, the plurality of openings 18 consist of eight (8) rows of four(4) openings each; however, any number of openings can be used and inany pattern including random placement. Preferably the plurality ofopenings are spaced evenly based on the cross-sectional area of biomassabove them to allow a more uniform liquid recovery system 70 and gasdistribution system 30.

The lower end 12 of the vessel 10 can have numerous openings 18 so thatthe lower end may be thought of as perforated or resembling a sieve orgrate.

As shown, the lower end may further comprise at least one screen 19 usedto cover the plurality of openings 18. The at least one screen is usedto prevent the biomass in the vessel 10 from passing through any of theplurality of openings 18 and getting into the liquid collection system70 or the gas distribution system 30.

In FIG. 6, the at least on screen 19 is shown as individual screenscovering each opening; however, a single screen may be used to cover allthe openings or any combination thereof. For example, the at least onescreen can consist of a couple of screens each covering a few openingsof the plurality of openings 18.

The wires of the at least one screen 19 can be oriented in any directionin the final form; however, the wires of the at least one screen 19 arepreferably oriented so that they run in the direction of material flowduring removal. In the case of a conically shaped lower end 12, wherematerial removal occurs at the apex, the wires of the at least onescreen 19 would preferably run in a direction from the base perimetertowards the apex. This orientation is preferred in order to prevent theat least one screen 19 from resisting material removal. If the wires ofthe at least one screen do not run in the direction towards the openingfor material removal, they may act like a grate, making material removaldifficult. Further, material removal is more likely to cause damage tothe wires of the at least one screen 19 if the wires are not oriented inthe direction of material removal.

FIG. 7 illustrates a cross section of a screen as used in FIG. 6. Asshown in FIG. 7, the screen is a wedge wire screen. This is preferablebecause any biomass particles that do penetrate the screen will bereleased by the tapered wedge wire and prevented from obstructing thescreen openings and thus be kept from impeding the gas or liquid flow.Although a wedge wire screen is preferable, other types of screens canbe used including a wire screen, a mesh screen, a membrane, a filter, orany other device that can prevent the biomass from obstructing any ofthe plurality of openings 18, and limit the contamination of the liquidrecovery system 70 and the gas distribution system 30.

FIG. 8 illustrates a cross section of a manifold for attaching theliquid recovery system 70 and the gas distribution system 30 to thelower end of the vessel 10. The gas distribution system 30 and theliquid recovery system 70 are preferably in communication with the lowerend 12 of the vessel 10 through the plurality of openings 18. In orderto allow easy attachment for communication, a plurality of manifolds 17may be used. The manifold 17 may be affixed to the lateral wall of thelower end 12 of the vessel 10. The manifold may be welded in place orattached using fasteners but should be sealed to the lower end 12 toprevent any gas or liquid leaks. As shown the manifold 17 contains twoports 22 and 23; however, any number of ports can be used. The ports 22and 23 are used to connect the gas distribution system 30 and the liquidrecovery system 70.

As shown in FIG. 6, the gas distribution system 30 will be incommunication with port 22 above port 23 in communication with theliquid recovery system 70. Having the gas distribution system 30 abovethe liquid recovery system 70 is preferable because the effluentdischarge entering the manifold 17 through one of the plurality ofopenings 18 will naturally gravitate toward the bottom of the manifold17 and port 23 in communication with the liquid recovery system. Thiswill prevent the effluent discharge from entering the gas distributionsystem 30.

Also, at least one screen 19, may be used to cover the plurality ofopenings 18 to prevent the biomass from entering the manifold and thusthe liquid recovery system 70 or the gas distribution system 30. Thediameter of the ports 22 and 23 is preferably large in proportion to thegap between the wires of the screen to prevent any biomass that passesthrough the screen 19 from obstructing the flow of gas or liquid. Inaddition, a gap should be left between the screen 19 and the ports 22and 23 to allow biomass that is too small to be blocked by the screen,to pass through and not clog the screen and cut off gas and liquid flow.

As shown in FIG. 8, the at least one screen 19 can be held in place by asleeve 21. The sleeve 21 is inserted inside the manifold 17 and holdsthe at least one screen 19 up against the plurality of openings 18. Theat least one screen 19 is beveled to fit flush with surface of vessel10. The use of the sleeve 21 prevents the at least one screen 19 frombeing permanently attached and therefore allows the screen to be removedand cleaned. While a sleeve 21 is shown in FIG. 8 the screen may be heldin place in other ways such as welding, clamping, springs, bolts andscrews, or other hardware.

The ports are preferably mounted on a flange 15 attached to the manifold17. This allows the flange 15 to be easily removed for inspection andcleaning of the manifold 17 and the at least one screen 19.

FIG. 9 illustrates a plurality of manifolds 17 attached to a pluralityof openings 18 on the lateral surface of the lower end 12 of the vessel10.

While FIG. 6 and FIG. 9 depict a design of the lower end 12 of thevessel 10 that is solid with a plurality of round openings 18, the lowerend 12 can have numerous other designs. FIG. 10 illustrates aperspective view of the lower end 12 with a plurality of openings 18 anda plurality of horizontal channels 2. A portion of the lower end 12 hasbeen sectioned away to better show the horizontal channels 2.

FIG. 11 illustrates a perspective view of the lower end 12 with aplurality of openings 18 and a plurality of vertical channels 3. Aportion of the lower end 12 has been sectioned away to better show thevertical channels 3.

FIG. 12A illustrates a horizontally oriented panel frame constructionfor a conically shaped lower end of a bioreactor. While the lower end 12may be made from a solid piece, it may also be made using a panel framedesign. The frame of the lower end 12 holds a plurality of horizontalpanels 4. The plurality of horizontal panels 4 creates a plurality ofopenings 18 in the lower end 12 of the vessel 10. FIG. 12B illustrates apanel design for use in a horizontal panel frame designed lower end 12for a bioreactor 100. As shown in FIG. 12B, the plurality of panels 4have at least one screen 19 to prevent the biomass from entering intothe plurality of horizontal panels 4. The horizontal panels 4 areconnected to gas distribution 30 and liquid recovery systems 70.

FIG. 13A illustrates a vertically oriented panel frame construction fora conically shaped lower end of a bioreactor. The frame of the lower end12 holds a plurality of vertical panels 5. The plurality of verticalpanels 5 creates a plurality of openings 18 in the lower end 12 of thevessel 10. FIG. 13B illustrates a panel design for use in a verticalpanel frame designed lower end for a bioreactor. As shown in FIG. 13B,the plurality of vertical panels 5 have at least one screen 19 toprevent the biomass from entering into the plurality of vertical panels5. The at least one screen 19 is preferably oriented with the wiresrunning vertically because it allows for the material to be more easilyremoved from the vessel 10. If the wires are running in the horizontaldirection as in FIG. 12B the at least one screen 19 resists materialremoval and acts more like a grate when the biomass is removed. FIG. 13Cillustrates a perspective view of the at least one screen 19 of FIG.13B.

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 17. A method of performing static solid statefermentation, the method comprising the steps of: a. mixing a bulkingagent with a biomass to form a mixture; b. adding the mixture to astatic solid state bioreactor; b. irrigating the mixture with an aqueoussolution; c. flowing a gas through the mixture; and, d. maintaining amicroorganism supporting environment within the mixture by calculating aspecific heat of an aqueous solution flow, calculating a specific heatof a gas flow, and balancing the aqueous solution flow with the gasflow.
 18. The method according to claim 17, further comprising the stepof maintaining a ratio of mass flow per cross sectional area per unittime of the gas flow to the aqueous solution flow between 0.25 and 0.4.19. The method according to claim 17, further comprising the step ofadding an inoculum comprising at least one microorganism to the biomassprior to the step of mixing a bulking agent with a biomass.
 20. Themethod according to claim 19, further comprising the step of adding oneor more enzymes to the biomass prior to the step of adding an inoculumto the biomass.
 21. The method according to claim 20, further comprisingthe step of adding an antibiotic to the biomass prior to the step ofadding enzymes to the biomass.
 22. The method according to claim 17,further comprising the step of collecting the liquid solution from alower end of the biomass and recycling the liquid solution back on to anupper end of the mixture.
 23. The method according to claim 22, furthercomprising the step of treating the liquid solution to improve qualitybefore recycling the liquid solution back on to an upper end of themixture.
 24. The method according to claim 17, wherein the bulking agentmaintains a hydraulic conductivity of the mixture greater than 10⁻⁴cm/sec.
 25. The method according to claim 17, wherein the bulking agentlimits the gas flow back-pressure to less than 200 mm of water head. 26.The method according to claim 17, further comprising the step ofreversing the direction of a gas flow through the mixture. 27.(canceled)
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